It is known in the prior art to test integrated circuit chips and the like by bringing an array of parallel wires into contact with numerous contact pads formed on the chips so as to make a reliable electrical connection therewith. This array of wires is called a probe contactor in the art. The pads may differ in height. Accordingly, the probes are allowed to bend or buckle a bit so that all the probes engage their corresponding pads with a good, solid, low resistance, contact force. Hence, the arrays are called buckling beam probe contactors.
One example of a buckling beam contactor is shown in U.S. Pat. No. 3,806,801 to Bove. The probe wires pass through the holes in a pair of perforated plates. The pair of perforated plates have holes in the correct positions to locate the array of probes so that they will contact the particular arrangement of pads on the chip to be tested. It may be necessary to use hundreds of parallel probe wires packed very close together. Thus, when the probes buckle, they may touch each other, interfering with the bending, or even shorting out. To avoid this problem, Bove insulates the probes and further offsets or slants the holes in the lower perforated plate to encourage all of the probe wires to buckle in the same horizontal direction.
Another buckling beam probe contactor is shown in U.S. Pat. No. 4,506,215 to Coughlin wherein a third intermediate perforated plate is used to induce a prebow in the probe beams. However, a centerpost is required to keep the top and bottom plates aligned and this centerpost severely limits the possible positions of the contact pads.
U.S. Pat. No. 4,843,315, to Bayer et al, shows a stack of perforated plates with myriad oblong holes to not only keep all of the probes isolated, but also to force multiple small bends in the probes so as to accommodate a greater range of pad heights with less total horizontal displacement. However, the extreme complexity of this structure, and the likelihood of a great deal of friction and rubbing in the holes is apparent, especially considering that hundreds of probes may be required, located only fractions of a millimeter apart. The probes could frictionally lock in one of the many holes and effectively become much shorter. This increases the contact force unpredictably which may damage the contact pads.
An entirely different approach may be seen in U.S. Pat. No. 4,932,883, to Hsia et al, where buckling beams are eliminated completely, and instead contact pads are substituted which rest on a springable elastomer to accommodate height differences. This approach does not allow a very dense array of contacts to be designed and the invention is really targeted more at the interconnection of integrated circuits with each other.
As integrated circuits become more and more complicated, with millions of circuits, while simultaneously shrinking in size, it is a necessity to have a probe contactor with very many probes very close together. This contactor should be more reliable than Bove, denser than Hsia et al and Coughlin, and much simpler than Bayer et al. The present invention achieves these objectives, and does so at a lower cost.